1. Field of the Invention
The present invention generally relates to a capacitor and, more particularly, to a capacitor containing at least two anodes and an intermediate cathode. The anodes are connected to a common terminal that is electrically isolated from the capacitor casing to which the cathode is electrically connected.
2. Description of Related Art
As more and more medical applications are investigated and implemented to aid and assist the human body, devices needed to deliver the desired therapy are becoming increasingly more sophisticated, both functionally and in terms of their structural makeup. Modern implantable devices require power sources that are smaller in size, but powerful enough to meet the therapy requirements. For example, a cardiac defibrillator has a battery powering circuits performing such functions as, for example, the heart sensing and pacing functions. This requires electrical current of about 1 microampere to about 100 milliamperes. From time-to-time, the cardiac defibrillator may require a generally high rate, pulse discharge load component that occurs, for example, during charging of a capacitor assembly in the defibrillator for the purpose of delivering an electrical shock to the heart to treat tachyarrhythmias, the irregular, rapid heartbeats that can be fatal if left uncorrected. This requires electrical current of about 1 ampere to about 4 amperes.
The current trend in medicine is to make cardiac defibrillators, and like implantable devices, as small and lightweight as possible without compromising their power. This, in turn, means that capacitors contained in these devices must be readily adaptable in how they are connected to each other as well as to the battery and the device circuitry. In that light, a number of patents and publications disclose electrical energy storage devices including capacitors having a dual anode structure.
One is described in U.S. Pat. No. 7,483,260 to Ziarniak et al., which is assigned to the assignee of the present invention and incorporated herein by reference. This patent relates to a design that provides first and second anodes electrically connected to each other within the casing, a cathode, and a working electrolyte. The anodes are electrically connected in parallel by an anode wire extending between them. A feedthrough wire extending outside the casing and electrically isolated therefrom is electrically connected to this anode wire intermediate the first and second anodes. The cathode is disposed between the first and second anodes and includes a tab extending from the cathode current collector. The cathode current collector tab is then tack welded to the inside surface of a casing side wall to electrically connect the cathode to the casing. The casing member to which the cathode current collector tab is tack welded is then secured to a second casing member to provide a hermetically sealed casing.
While the Ziarniak et al. capacitor construction is completely acceptable, there is a need for greater flexibility in capacitor designs. This is driven, in part, by the myriad of applications described above. Instead of electrically connecting the cathode current collector tab to an internal location of the casing sidewall, the present design has the cathode tab electrically connected directly to the ferrule of the glass-to-metal seal (GTMS). Connecting the cathode current collector tab to the GTMS provides the designer with another option when building capacitors for a particular need that may not have been entirely met by the Ziarniak et al. design.